Streak-free windows: what actually causes streaks

Streaks on glass are not caused by the cleaning fluid, and no product on this wall will fix them on its own. They come from four things: a damaged blade, a dry blade, an overlapping error, or drying time. Each has a specific fix.

Cause one: a nicked or worn blade

This is by far the most common. A rubber blade has one working edge, and one nick in it leaves a fine line on every pass for the rest of the job.

Hold the blade up against a light and look along the edge. Any gap you can see will show on the glass. Any grit that gets dragged along the edge — sand, a chip of paint, dried mortar — will cut it, which is why a blade used on a building site lasts a fraction of the time.

The fix: keep the blade off gritty surfaces, wipe it before starting, and treat the blade as a consumable rather than part of the tool. A blade that has been used hard for a season is finished, whatever it looks like from a distance.

Rubber blades also take a set. Left standing on the edge in a bucket, the rubber curls and no longer meets the glass flat. Store the tool hanging or flat.

Cause two: a dry blade on dry glass

A squeegee is designed to slide on a film of water. Drag a dry blade across dry glass and it chatters, skips and leaves lines.

The fix: wet the whole pane first and keep it wet until the last pull. Professionals wet the blade itself before the first stroke for exactly this reason. On a hot day, work smaller sections so the glass has not dried before you reach it.

Cause three: the overlap

Every pass leaves a thin bead of water at the edge of the blade. If the next pass starts exactly where the last one ended, that bead is left behind as a line.

The fix: overlap each pass by an inch or two, and wipe the blade with a cloth between passes. The wipe matters as much as the overlap — a blade carrying water from the last pass deposits it at the start of the next.

For a small pane, one continuous S-shaped pull top to bottom avoids the problem entirely. For a large pane, horizontal passes working downwards, each overlapping the one above, is the standard method.

Cause four: drying too slowly at the edges

The last thin film at the edge of the glass and in the corners will dry on its own and leave a mark. That is what the cloth is for: run a dry microfibre or a lint-free cloth around the perimeter immediately after the last pull.

Detail the frame too. Water sitting in the frame wicks back onto the glass and leaves a line an hour later, long after you have decided the job went well.

The one product decision that does matter

Not the fluid — the blade width relative to the pane. A blade wider than the pane cannot be used at all; a blade much narrower turns one pull into five. For domestic windows a 10 to 14-inch blade covers most panes in one or two passes.

For very small panes, divided lights and car glass, a small hand squeegee is the right tool and is on the shelf for that reason.

Shower glass is a different problem

Shower doors are not dirty, they are limescale-marked. A squeegee used after every shower prevents the marks forming, which is a far easier job than removing them later.

The tool is different too: shorter, lighter, usually silicone rather than rubber, and often with a hook or a suction mount so it lives in the shower. Those are grouped separately under shower and bathroom squeegees.

Cold weather

Rubber stiffens as it gets colder and a stiff blade chatters. Below about forty degrees, expect to work in smaller sections and to wipe the blade more often. Silicone blades hold their flexibility further down the scale, which is the practical reason to pay more for one.

Order of work

Top to bottom, always — running water re-wets glass you have already done, so anything else means doing it twice. Do the inside and the outside in different directions, horizontal one side and vertical the other, and any streak that remains tells you immediately which side it is on.

Where to look on the shelf

Handheld and long-handled window tools, including the two-in-one sponge-and-blade types, are on the window and glass squeegees page. Shower work is on the shower and bathroom page, and if you are working on film or wrap rather than glass, the soft-edge tools are under vinyl and tint squeegees.

Every listing states the blade width, because that is the measurement that decides whether the tool fits the job.